先观察,然后想一想其中的规律.1 1 1 1--------- = ------- = ------ — -----2×3 6 2 31 1 1 1--------- = ------- = ------ — -------3×4 12 3 41 1 1 1--------- = ------- = ------ — -------4×5 20 4 51 1 1 1计算:---------- + ---------
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![先观察,然后想一想其中的规律.1 1 1 1--------- = ------- = ------ — -----2×3 6 2 31 1 1 1--------- = ------- = ------ — -------3×4 12 3 41 1 1 1--------- = ------- = ------ — -------4×5 20 4 51 1 1 1计算:---------- + ---------](/uploads/image/z/15218299-19-9.jpg?t=%E5%85%88%E8%A7%82%E5%AF%9F%2C%E7%84%B6%E5%90%8E%E6%83%B3%E4%B8%80%E6%83%B3%E5%85%B6%E4%B8%AD%E7%9A%84%E8%A7%84%E5%BE%8B.1+1+1+1---------+%3D+-------+%3D+------+%E2%80%94+-----2%C3%973+6+2+31+1+1+1---------+%3D+-------+%3D+------+%E2%80%94+-------3%C3%974+12+3+41+1+1+1---------+%3D+-------+%3D+------+%E2%80%94+-------4%C3%975+20+4+51+1+1+1%E8%AE%A1%E7%AE%97%EF%BC%9A----------+%2B+---------)
先观察,然后想一想其中的规律.1 1 1 1--------- = ------- = ------ — -----2×3 6 2 31 1 1 1--------- = ------- = ------ — -------3×4 12 3 41 1 1 1--------- = ------- = ------ — -------4×5 20 4 51 1 1 1计算:---------- + ---------
先观察,然后想一想其中的规律.
1 1 1 1
--------- = ------- = ------ — -----
2×3 6 2 3
1 1 1 1
--------- = ------- = ------ — -------
3×4 12 3 4
1 1 1 1
--------- = ------- = ------ — -------
4×5 20 4 5
1 1 1 1
计算:---------- + ------------ + --------------····················------------
2×3 3×4 4×5 99×100
先观察,然后想一想其中的规律.1 1 1 1--------- = ------- = ------ — -----2×3 6 2 31 1 1 1--------- = ------- = ------ — -------3×4 12 3 41 1 1 1--------- = ------- = ------ — -------4×5 20 4 51 1 1 1计算:---------- + ---------
1/2-1/3+1/3-1/4+1/4-1/5.+1/99-1/100=1/2-1/100=49/100
规律是1/(a乘b)=1/(b-a)乘(1/a-1/b) (a<b)